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>>Class 12
>>Physics
>>Ray Optics and Optical Instruments
>>Combination of Mirror and Lenses
>> $The focal length of a biconvex lens of r$

Question

The focal length of a biconvex lens of refractive index $\frac{3}{2}$ is 40 cm. When immersed in a liquid of refractive index $\frac{4}{3}$ its focal length in meters will be :

A

$160$

B

$16$

C

$1.6$

D

$0.8$

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Updated on : 2022-09-05

Solution

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Correct option is C)

Using lens makers formula and taking the ratio for the two cases, $\frac{f _{1}}{f _{2}} = (\frac{μ _{2} - 1}{μ _{1} - 1})$

$\frac{4 0}{f _{2}} = \frac{( \frac{3 / 2}{4 / 3} - 1 )}{( 3 / 2 - 1 )}$

$f_{2} = \frac{4 0}{2} \times \frac{8}{1} = 160 c m = 1.6 m$

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